Recently, in the technique of forming an image based on electrophotography, full color, high image quality, and high speed performance have been required. In accordance with these requests, there have been made technical developments such as coloring of toners, downsizing of particles of toners, establishment of low-temperature fixability and high-temperature offset resistance.
Recently, various proposals have been made as to techniques intended for improving the low-temperature fixability of toners, such as a technique using both polyester resin and low-melting wax and a technique using crystalline polyester. However, it is difficult to technically establish both of the low-temperature fixability and the high-temperature offset resistance, and so there have been discussed toners such as toners using polyester resin containing a gel component and toners whose molecular weight is regulated.
Furthermore, in order to realize a high-definition and high quality image, particles of toners are downsized. However, toners made of polyester resin with low grindability tend to require a larger amount of energy consumed in a pulverization process for downsizing particles. Furthermore, there is a problem that although a large amount of energy is consumed for pulverization, only toner particles whose particle size distribution is wide can be obtained.
In order to reduce energy consumed in the pulverization process and obtain toner particles whose particle size distribution is narrow, there have been discussed additives such as a grinding aid and a plasticizer and an adding method. For example, Patent Literature 1 describes that binder resin contains at least carboxyl group-containing vinyl resin and glycidyl group-containing vinyl resin and contains 5 to 50% by mass of a THF insoluble component in binder resin components of toner. It is reported that this allows low-temperature fixation regardless of a configuration of a fixing device, allows excellent high-temperature offset resistance, prevents occurrence of image defect due to time lapse or being left unattended, and allows a stable and high image quality regardless of whether the toner is used under a low moisture or a high moisture.
Furthermore, Patent Literature 2 describes (1) binder resin for color toners, wherein the binder resin comprises at least carboxyl group-containing vinyl resin (C), glycidyl group-containing vinyl resin (E) and a reaction product thereof, a content of a THF insoluble gel portion is less than 1 mass %, and a softening point is not more than 130° C., and (2) binder resin for color toners, wherein a storage modulus G′ at 160° C. is not less than 50 Pa and less than 10,000 Pa measured at a frequency of 6.28 rad/sec. It is reported that such binder resin allows providing a color toner which has excellent gloss and is suitable for a color toner.